CAIE IGCSE Physics Isotope Choice for Practical Uses
Practise selecting an emission type and half-life for smoke alarms, thickness control, sterilisation, food irradiation and medical diagnosis or treatment.
- Syllabus
- 2026–2028
- Course
- Physics 0625
Exam points
- choose ionising short-range alpha for smoke alarms and explain smoke reducing the ionisation current
- choose beta for thickness control because partial absorption changes with paper or aluminium thickness
- choose penetrating gamma and a task-appropriate half-life for sterilisation, tracers or cancer treatment
5.2.4.3—Isotope choice using radiation type question 1
[Maximum number: 2]
Many household smoke alarms contain a sample of the radioactive isotope americium-241 (Am).
Americium-241 decays to an isotope of neptunium (Np) by alpha-particle ( α-particle) emission.
The isotope of neptunium produced by americium-241 is also radioactive.
The decay of this isotope of neptunium produces an isotope of protactinium which decays by β-emission. β-particles are more penetrating than α-particles.
The half-life of neptunium is longer than two million years.
Using this information, explain the advantage of this long half-life for the use and safe disposal of a household smoke alarm.
Low(er) (initial) activity OR Few emissions per unit time
M1
so smoke detectors are not hazardous to humans OR so disposal of old detectors is cheap / easy
A1
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